// first-order lag derivative term
(*
  Parameter K must be set to T / (T + T1)
*)
FUNCTION_BLOCK DT2

VAR_INPUT
  IN : REAL;
  K : REAL;
END_VAR
VAR_OUTPUT
  Q : REAL;
END_VAR
VAR
  H : REAL := 0.0;
END_VAR

BEGIN
  Q := IN - H;
  H := H + K * Q;
END_FUNCTION_BLOCK